I disagree on some of your stuff, guest Tony.

There is some format though it is not purely bill Monroe's. You can have an act like Del Mcourey open for the Juliard String Quartet. Same audience, different music.

Doc Watson is certainly more than a folksinger. He can be a pure bluegrass player as he was on the Strictly Instrumental album he recorded years ago with Flatt & Scruggs as well as with Scruggs and Skaggs on their 3 pickers album. He also recorded an album of rockabilly music so I guess he's a rockabilly singer, also.

Jerry Garcia as I pointed out has done much bluegrass either with Old & In the Way or bluegrass flavored hillbilly jazz with David Grisman.

On the other hand, foggy Mountain Breakdown played on trombones is hardly bluegrass, so the instruments DO matter.

However, if you played Foggy Mountain Breakdown on a trombone with the right ATTITUDE....................